The present invention relates to a target tracking system. In particular, the present invention relates to a single receiver wireless locating and tracking system.
Wireless locating and tracking systems are often used to identify the location of a target object. Conventional wireless locating systems typically employ two or three wireless receivers positioned at known co-ordinates for the identification a target object""s location. For instance, two-dimensional global positioning systems (GPS) employ three satellites which transmit their respective co-ordinates and transmission times to a GPS receiver. Typically, additional satellite are used for redundancy purposes, to increase accuracy and for three-dimensional imaging. The GPS receiver receives the transmitted information, and then determines its position from the transmitted co-ordinates and from the transmission interval of the wireless transmissions from the satellites to the GPS receiver. Signal strength locating systems typically employ two wireless receivers positioned at known co-ordinates for receiving wireless transmissions from a wireless transmitter. The co-ordinates of the wireless transmitter, relative to the wireless receivers, are calculated from the signal strength of the wireless transmission received at each receiver. Although both forms of locating systems, particularly signal strength locating systems, are widely used, they suffer from a number of deficiencies.
For instance, GPS satellites intermittently transmit erroneous information to the GPS receivers. Although military users of GPS receivers are provided with an encryption key for identifying and removing the erroneous information, the encryption key is not available to non-military GPS users. As a result, GPS systems do not provide non-military GPS users with particularly accurate co-ordinate identification. Further, triangulation by RF signal strength is limited by the effects of co-channel interference, multi-path distortion, tropospheric scatter, phase distortion and signal phase cancellation. Additionally, the multiple satellites/receivers required of both forms of wireless systems constitute significant barriers to market entry. Attempts have been made to improve upon the conventional wireless locating systems.
For example, Jarvis (U.S. Pat. No. 3,665,312) teaches a wireless locating system comprising a multiple frequency wireless transmitter, an entry detector for activating the wireless transmitter upon detection of unauthorized entry, and a plurality of directional receivers. Once unauthorized entry is detected, the wireless transmitter transmits a unique coded signal to the directional receivers for co-ordinate identification using signal triangulation. To thwart jamming of the wireless transmitter, the transmitter sequentially shifts its transmission frequency at predetermined time intervals. However, Jarvis is limited by the need for multiple directional receivers.
Regan (U.S. Pat. No. 4,177,466 assigned to Lo-Jack Corporation) teaches an auto theft detection system comprises a wireless transceiver configured with the vehicle identification number of the vehicle in which the transceiver is fitted, and a plurality of mobile radio direction finders for determining the direction of a transmission from the target transceiver. If the vehicle fitted with the target transceiver is reported stolen, a transmitter station transmits a continuous locator signal encoded with the vehicle identification number assigned to the subject transceiver. Upon receipt of the continuous locator signal, each transceiver decodes the signal to determine whether the transmitted vehicle identification code matches its assigned vehicle identification number. The transceiver having the matching vehicle identification number transmits a responsive output signal which the radio direction finders use to triangulate on the subject vehicle. Although the use of multiple mobile radio direction finders reduces the sensitivity of the system to co-channel interference, multi-path distortion, phase distortion and signal phase cancellation, the system can be defeated by jamming the transmission of the wireless transmitter with an RF transmitter tuned to the appropriate transmitting frequency. Further, recourse to multiple mobile direction finders unnecessarily increases the cost of locating a stolen vehicle.
Rackley (U.S. Pat. No. 4,742,357) teaches a vehicle locating system comprising a target wireless transceiver configured with the vehicle identification number of the vehicle in which the transceiver is fitted, and a single conventional directional receiver for receiving a transmission from the target transceiver. Each wireless transceiver is capable of operating in a direction-triangulation mode, a distance-triangular mode, a distance-direction mode, and long range navigation (LORAN) mode. If the vehicle fitted with the target transceiver is reported stolen, a base station transmits to the target transceiver a data packet containing the subject vehicle""s vehicle identification number, a location mode code identifying distance-direction mode as the operating mode for the transceiver, and a code identifying the transmission frequency at which transceiver is requested to transmit. Upon receipt of the base station message, the transceiver configured with the subject vehicle identification number activates its echo channel. The base station then transmits an echo pulse to the transceiver and activates a timer. After the transceiver receives the echo pulse, it returns the echo pulse back to the directional receiver through the echo channel, after a precise fixed delay. The directional receiver calculates the distance of the vehicle relative to the receiver from the propagation delay of the echo pulse, after subtracting the fixed delay of the transceiver. Simultaneously, the directional receiver measures the angle of transmission of the echo pulse from the transceiver, and converts the calculated range and angle measurements to map coordinates. Although Rackley is advantageous in that it only requires a single directional receiver, the need for the wireless transceiver to operate in a number of different operation modes increases the cost and complexity of each transceiver. Further, as the delay of the transceiver can vary with temperature and humidity, the accuracy of the calculated co-ordinates is limited. In addition, the use of a single conventional directional receiver exposes the locating system to further inaccuracy from multi-path distortion, signal phase cancellation, and ambient noise.
Therefore, there remains a need for a target tracking and locating system which does not rely on a plurality of wireless directional receivers for accurate target co-ordinate location. Further, there remains a need for a target tracking and locating system whose accuracy is not sensitive to RF jamming, multi-path distortion and changes in environmental conditions.
According to a first aspect of the present invention, there is provided a single receiver wireless tracking system which addresses deficiencies of the prior art wireless target tracking and locating systems. The wireless tracking system includes a wireless target including a wireless communication system for transmitting a data packet over a communication path, and a locating station for determining a position of the target. The data packet transmitted from the target includes an identification code uniquely associated with the target. The locating station includes a configurable directional antenna, a communication interval processing system, a direction processing system, and a position processing system. The communication interval processing system is in communication with the directional antenna and determines the transmission interval (elapsed transmission time) of the transmitted data packet over the communication path. The direction processing system determines the transmission angle (angular direction) of the communication path, and is in communication with the directional antenna for controlling the configuration of the directional antenna so as to facilitate the determination of the transmission angle. The position processing system is in communication with the interval processing system and the direction processing system, and determines the target position from the identification code, the transmission interval and the transmission angle.
In accordance with the first aspect of the invention, there is also provided a method for locating a target which includes the steps of (1) configuring a configurable directional antenna for determining a transmission interval and a transmission angle of a data packet transmitted from a target over a communication path; (2) receiving the data packet with the configured directional antenna, the received data packet including an identification code uniquely associated with the target; (3) determining the transmission interval and the transmission angle of the received data packet; and (4) determining a position of the target from the identification code, the transmission interval and the transmission angle.
According to a second aspect of the invention, there is provided a wireless locating station for determining a position of a target, which addresses deficiencies of the prior art wireless locating stations. The wireless locating station includes a configurable directional antenna for receiving over a communication path a data packet from the target, a communication interval processing system in communication with the directional antenna, a direction processing system in communication with the directional antenna, and a position processing system in communication with the interval processing system and the direction processing system. The data packet transmitted from the target includes an identification code uniquely associated with the target. The communication interval processing system determines the transmission interval of the transmitted data packet over the communication path. The direction processing system determines the transmission angle of the communication path, and controls the configuration of the directional antenna so as to facilitate the determination of the transmission angle. The position processing system determines the target position from the identification code, the transmission interval and the transmission angle.
According to a third aspect of the invention, there is provided a wireless target for use with a wireless locating station for identifying a position of the wireless target, which addresses deficiencies of the prior art wireless targets The wireless target includes a data transceiver for transmitting a data packet over a communication path, and a loop-through system in communication with the data transceiver for transmitting the data packet in response to a data key received from the locating station. The loop-through system includes a propagation delay processing system for determining the propagation delay through the target and for providing the locating station with an indication of the identified propagation delay.
According to a fourth aspect of the invention, there is provided a configurable directional antenna which addresses deficiencies of the prior art antennae. The configurable directional antenna includes a centre antenna element, and a plurality of second antenna elements disposed about the centre antenna element. Each second antenna element defines, together with the centre antenna element, an antenna sector which facilitates communication of electromagnetic energy. The configurable directional antenna also includes a switch matrix for altering a configuration of each antenna sector.
In accordance with a preferred embodiment of the invention, the locating station includes a data transmitter for transmitting to the target a data key uniquely associated with the target, and a data receiver for receiving the data packet from the target in response to the data key. The communication interval processing system of the locating station includes an interval counter in communication with the data transmitter and the data receiver. The wireless communication system of each wireless target includes a data transceiver, and a loop-through system in communication with the data transceiver for transmitting the data packet in response to the data key received from the locating station. The loop-through system includes a propagation delay processing system for determining a propagation delay through the target and for providing the data packet with a data field identifying the propagation delay. The communication interval processing system determines the transmission interval between the target and the locating station in accordance with the propagation delay, a transmit time of the data key, and a receipt time of the data packet.
The loop-through system of the wireless target also includes a reference clock for clocking the data packet through the data transceiver, and a symbol correlator coupled to the reference clock and the data transceiver for receiving a clock synchronization symbol from the locating system. The symbol correlator synchronizes the clocked data packet with a system clock of the locating system in accordance with the received clock synchronization symbol. The direction processing system of the locating station includes a phase detector for determining the phase of the received data packet relative to the system clock, and an amplitude detector for determining the amplitude of the received data packet. The position processing system of the locating station includes a signal processing system in communication with the phase detector and the amplitude detector for deriving the transmission angle from the phase and the amplitude.
The configurable directional antenna comprises a monopole array which includes a centre antenna element in communication with the communication interval processing system and the direction processing system, a plurality of second antenna elements disposed about the centre antenna element. Each second antenna element, together with the centre antenna element, comprises an antenna sector, with each antenna sector defining an antenna lobe. A first portion of the second antenna elements is disposed at an inner radius about the centre antenna element, and a second portion of the second antenna elements is disposed at an outer radius about the centre antenna element, such that each antenna sector includes one of the radially inner second antenna elements, one of the radially outer second antenna elements, and a conductor extending between the respective radially inner and outer second antenna elements. The monopole array also includes a switch matrix coupled to each antenna sector for altering the shape and gain of the antenna lobe pattern.
The position processing system of the locating station is in communication with the switch matrix for altering each antenna lobe configuration as necessary to obtain the desired tracking resolution. The signal processing system of the position processing system includes an ambient noise database identifying ambient noise surrounding the monopole array, and a signal processor in communication with the ambient noise database for determining the target position with reference to the ambient noise.